Material cooler with recycling of cooling gas

ABSTRACT

A cooler for hot material such as cement clinker with an arrangement for recycling cooling air. The cooler includes a housing divided into an upper material chamber and a lower plenum chamber by a gas permeable grate which supports and advances the material through the material chamber. Ambient cooling air is blown through the hottest and the coolest material. Two air recirculation circuits are employed. The ambient air blown through the coolest material is divided so that a portion goes to each recirculation circuit. One recirculation circuit returns air to the plenum chamber at a point where it will pass through the material to be cooled and then be conducted to the furnace. The other recirculation circuit returns air to the plenum chamber at points where it will pass through the material and some of it will be conducted to a furnace, while the remaining air will be returned to the recirculation circuit. An indirect heat exchanger is mounted in one of the recirculation circuits.

United States Patent Devel Dec. 5, 1972 Primary Examiner-Kenneth W.Sprague Assistant Examiner-James C. Yeung Attorney-Jack L. Prather [72]lnventor: Daniel T. Devel, Le Perreux, France [73] Assignee: FullerCompany, Catasauqua, Pa. ABSTRACT [22] Filed; on, 27, 1971 A cooler forhot material such as cement clinker with an arrangement for recyclingcooling air. The cooler [21] Appl' l93027 includes a housing dividedinto an upper material chamber and a lower plenum chamber by a gas [30]Foreign Application Priority Data Pe meable grate which supports andadvances the material through the material chamber. Ambient cool- NOV.6, 1970 France ..7040103 is blown through the hottest and the coolestmaterial. Two air recirculation circuits are employed. [52] US. Cl..34/164, 263/44, 263/53 R The ambient air blown through the coolestmaterial is [51] Int. Cl ..F26b 9/00 divided so that a portion goes toeach recirculation [58] Search 263/32 53 circuit. One recirculationcircuit returns air to the plenum chamber at a point where it will passthrough [56] References C'ted the material to be cooled and then beconducted to UNITED STATES PATENTS the furnace. The other recirculationcircuit returns air to the plenum chamber at points where It will pass2,587,378 2/1952 Petersen ..263/44 through the material and some of itbe conducted 2,846,778 8/ 1958 Marklemi r to a furnace, while theremaining air will be returned 3,276,755 10/1966 Bast t R to therecirculation circuit. An indirect heat 3,522,012 7/1970 Blann Rexchanger is mounted in one of the recirculation ircuits.

10 Claims, 3 Drawing Figures '2' \ea kloz 70 3 33 74 8 w 0V MO} {10353 esA L'QJJQWSQOIIM 45 47 49 32 Q 42 ififiiq 5 iiszi: 56

P'A'TEN'TEDnEc 51912 FIG. 3

R l4 l2 PRIOR ART IS LE] U PRIOR ART MATERIAL COOLER WITH RECYCLING OFCOOLING GAS BACKGROUND OF THE INVENTION This invention relates tocoolers for hot particulate materials such as hot cement clinker. Moreparticularly, this invention relates to a cooler for particulatematerial which employs a recycling of the cooling gas.

Prior to the present invention, it was known to cool hot material suchas cement clinker which is discharged from a furnace such as a rotarykiln by supporting a bed of the material on a gas permeable grate andblowing air through the grate and bed of material. The grate arrangementis used to advance the material through the cooling apparatus. One suchcooler is shown in U. S. Pat. No. 2,846,778 which employs a plurality ofalternately movable and stationary grates for advancing the materialthrough the cooler.

The prior art cooler described in U. S. Pat. No. 2,846,778 has theadvantage of air quenching cement clinker as it is discharged from arotary kiln, and the further advantage that a portion of the cooling airwhich is heated as it cools the hot cement clinker from a temperature ofabout 2500 F to about 150 F can be returned to the furnace as combustionair. Since this air is already heated, the system can result insubstantial fuel savings in the cement making process.

A particular disadvantage of the arrangement shown in the abovementioned prior patent is that only a portion of the air needed forcooling the hot material can be returned to the furnace. The remainingair must be exhausted to atmosphere. However, as the cooling air passesthrough the hot material, it entrains dust and solid materials whichmust be removed from the exhausted air in order to avoid polluting theatmosphere. In order to remove these pollutants, high efficiency dustcollectors such as bag houses or electrostatic precipitators must beused. These high efficiency collectors add great expense to a coolerinstallation.

In the past, it has also been suggested to recirculate that portion ofthe cooling air which is not sent to the furnace as combustion air.However, recirculation systems that have been proposed prior to thepresent invention have substantially reduced the ability of the coolerto cool the hot material. Although it has been proposed to add a heatexchanger to the recycle circuit, the ability of the cooler to cool hotmaterial is still less than desirable.

SUMMARY It is the principal object of this invention to provide anapparatus for cooling hot particulate material such as cement clinkerwhich retains the advantages of prior cooling apparatus yet eliminatestheir disadvantages.

It is another object of this invention to provide a cooling apparatusfor hot material which substantially reduces or eliminates the necessityof employing high efficiency dust collectors while maintaining theability of prior art apparatus to cool hot material.

In general, the foregoing and other objects will be carried out byproviding apparatus for cooling hot particulate material such as cementclinker discharged from a furnace such as a kiln comprising a housinghaving an inlet for material to be cooled and an outlet for cooledmaterial; porous grate means mounted in and dividing said housing intoan upper material chamber and a lower plenum chamber; said porous gratemeans being adapted to support a bed of material in the materialchamber; means dividing the plenum chamber into a plurality ofcompartments; first blower means for supplying ambient cooling gas to atleast one of said compartments for passage through said porous gratemeans and the bed of material for cooling the material; firstrecirculation means for exhausting at least some of the ambient coolinggas from said material chamber after it passes through the material andrecirculating it to at least one of said compartments for passagethrough the porous grate and material for cooling the material; andsecond recirculation means for exhausting at least some of the ambientcooling gas from said material chamber after it passes through thematerial and recirculating it to at least one of said compartments forpassage through the porous grate and material for cooling the material;said second recirculation means being adapted to exhaust from saidmaterial chamber at least some of the cooling gas which has beenrecirculated through said second recirculation means whereby a mixing ofambient cooling gas and recirculated cooling gas is achieved. 1

BRIEF DESCRIPTION OF THE DRAWING The invention will be described inconnection with the annexed drawing wherein:

FIG. 1 is a diagrammatic view of one form of the prior art;

FIG. 2 is a diagrammatic view of another form of the prior art; and

FIG. 3 is a generally diagrammatic view of the cooling apparatus of thepresent invention.

DESCRIPTION OF THE PRIOR ART Referring to FIG. 1, there is shown acooler for hot material such as cement clinker which has been in use forsome time and may be of the type shown in U. S. Pat. No. 2,846,778. Itincludes a housing 1 which is divided into an upper material chamber 3and a lower plenum chamber 4 by means of a porous grate means 6. Thegrate means 6 may be of the type shown in the above mentioned patent andincludes a plurality of alternately stationary and reciprocating gratesfor supporting a bed 8 of particulate material to be cooled andadvancing the material through the cooler. The cooler is provided with amaterial inlet 10 for receiving hot material from a furnace such as arotary kiln (not shown). The cooler also includes an outlet 12 forcooled material.

The plenum chamber is divided into a plurality of compartments andambient cooling air is supplied to these compartments from suitableblowers (not shown) as indicated by the arrows 14. The cooling airpasses through the'porous grates and material bed to cool the material.

As the air passes through the bed of material, it is heated by the hotmaterial. A portion of this air is directed toward the kiln ascombustion air as designated by the arrow 15. The remainder of the airis exhausted to atmosphere from the cooler through an exhaust conduit 16as shown by arrow 17.

It has been found that the amount of air which is required to coolcement clinker is about three times the amount of combustion air whichcan be used by the rotary kiln used in the clinkering process. Thus, ifthe amount of air needed to cool the clinker is taken as 3N and theamount of air which can be used by the kiln is 1N, then the amount ofair exhausted to atmosphere is 2N.

As the cooling air passes through the bed of material, it entrains dustand solids which must be removed before the air is exhausted toatmosphere. In order to comply with pollution control laws, it isnecessary to use high efficiency dust collectors. The large quantity ofair as represented by 2N which must pass through the high efficiencycollectors necessitates a very large dust collection system which cancost as much as the cooler.

in FIG. 2, there is shown a prior art arrangement which attempts toeliminate the dust collection system by recirculating the air whichwould be vented to atmosphere in the system of FIG. 1. The cooler itselfis similar to that of FIG. 1 and like parts have been designated withlike numerals.

In the arrangement of FIG. 2, ambient cooling air is blown through thecoolest material in the cooler as indicated by arrow by blowers (notshown). This air is exhausted through exhaust conduit 16 and conductedby a suitable conduit 22 to be blown through the hottest zone of thecooler 1 as indicated by arrow 21. This air is then returned to the kilnas combustion air as indicated by arrow 23.

With the system shown in FIG. 2, half the air used is returned to thekiln, which is fixed at 1N because that is the maximum air which can beused by the kiln. Thus, the total air which flows through the materialto cool the material is 2N if a closed system is to be maintained.However, in order to properly cool some materials such as cementclinker, it is advantageous to maintain the ratio of total air throughthe bed to the air returned to the kiln higher than two, and preferablythree.

DESCRIPTION OF THE PREFERRE EMBODIMENT in order to provide a closedsystem wherein the ratio of total air through the bed to fresh air orair returned to the kiln is three, I have provided the arrangement shownin FIG. 3.

Referring to FIG. 3, the material cooling apparatus of the presentinvention is generally indicated at 30. The cooler includes a gaspermeable grate means 32 dividing the housing into an upper materialchamber 34 and a lower plenum chamber 36. The porous grate means may besimilar to that shown in U.S. Pat. No. 2,846,778 and serves to support abed 33 of material to be cooled and advance the material through thecooler.

The housing is provided with a material inlet 38 for receiving materialto be cooled such as cement clinker from a furnace such as a rotary kiln(not shown). The housing also includes a material outlet 40 fordischarging cooled material from the apparatus. A breaker 42 of anywell-k nown type is positioned in the outlet 40.

The plenum 36 is divided into a plurality of compartments 44, 46, 48,50, 52 and 54 by divider means 45, 47, 49, 51 and 53. Blowers 56, 58,60, 62, 64 and 66 are flow connected to the compartments 44, 46, 48, 50,52 and 54 respectively for supplying cooling gas to the plenum 36 forpassage through the porous grate 32 and bed of material 33 to cool thematerial.

The material chamber 34 may be considered to be divided into three zones70, 72 and 74 and indicated by the broken lines. There is no actualphysical division of the chamber 34. The zone 70 represents the zone ofhottest material, the zone 74 represents the zone of coolest material,and the zone 72 has material of intermediate temperature.

Ambient cooling air is supplied by blower means 56 and compartment 44 tothe hottest zone 70 to provide an initial air quench of the hot materialadmitted to the cooler. This air is heated by the hot material andreturned to the furnace as combustion air through a suitable conduitsuch as material inlet 38 as shown by arrow 76.

Ambient cooling air is also supplied by blower means 66 and compartment54 to the coolest zone 74 and to the intermediate zone 72. This ambientair serves to achieve the final cooling of the material.

Some of the air which passes from compartment 54 through the porousgrate 32 and bed of material is exhausted from the zone 74 of chamber 34through an outlet 78 and a first recirculation system 80 which includesa duct 81 connected to a dust collector 82. A stack 84 with a controldamper 86 may be provided to permit adjustment during start-up periodsand to ensure operational safety in case of irregular material feed orunstable conditions. From the dust collector 82, the recirculated air issupplied to blower means 58 by duct 88. A bleed input valve 87 may beprovided to add cool ambient air to the recirculated air during start-upand periods of unstable operation. From blower means 58, therecirculated air is directed into zone 70 and after passing through thehot material, is conducted to the furnace as hot combustion air alongwith the air supplied by blower means 56.

That portion of the ambient cooling air supplied by blower 66 whichpasses into intermediate zone 72 is exhausted from the material chamber34 to a second recirculation means generally indicated at 90. The secondrecirculation means 90 includes a hood 92 mounted in the zone 72 forcollecting cooling air which passes through the material in that zone. Aduct 94 is flow connected to the hood 92 and conducts the exhausted airto dust collector 96. A bleed valve 95 may be provided for admittingcold air during start-up and periods of unstable operation.

Air discharged from the collector 96 is divided into three parts in theembodiment shown as illustrated by conduits 98, 99 and 100. An indirectheat exchanger 102 is mounted in each of the ducts 98, 99 and 100 forcooling the air exhausted from the intermediate zone 7 2. The ducts 98,99 and 100 supply the thus cooled air to blowers 60, 62 and 64,respectively. 8

Air supplied by blowers 62 and 64 to compartments 50 and 52,,respectively, passes through the grate 32 and material 33 in theintermediate zone 72 and is exhausted from the chamber 34 by hood 92 ofthe second recirculation means 90 and is mixed therein with ambientcooling air from blower 66 and compartment 54. Air supplied by blower 60to compartment 48 passes through the grate means and material bed and isexhausted from chamber 34 partially through the second recirculationsystem 90 and partially through the material inlet 38 to the furnace.

From the foregoing, it can be seen that the compartments 44 to 54 andpartitions 45 to 53 are positioned so that there is a mixing of ambientcooling air and recirculated cooling air. This mixing of the cooling airinsures a renewal of the cooling air and a continuous operation of thesystem.

An example of the cooler system will now be given which is designed tocool 1500 tons of material per day.

The temperature T of air in zone 70 is about 870 C; the temperature 0 ofair in zone 72 is about 300 C; and the temperature t of air supplied tocompartment 46 is about 120 C.

The fans or blowers 56 to 62 have the following capacities:

Blower Capacity in Vol. in Nmlkg Temperature Number mlmin. of Clinker ofAir in C In the example given, it is believed that compartment 48received 0.45 Nm lkg air and delivers about 0.14 Nm lkg air to zone 70and about 0.31 Nm /kg air to zone 72. Compartment 54 receives a volumeof ambient air of 0.59 Nm /kg and is believed to deliver 0.14 Nm /kg tozone 72 and 0.45 Nm /kg to zone 74.

The mixing of ambient and recirculated cooling air may be illustrated bythe following table:

a housing having an inlet for material to be cooled and an outlet forcooled material;

porous grate means mounted in and dividing said housing into an uppermaterial chamber and a lower plenum chamber;

said porous grate means being adapted to support a bed of material inthe material chamber;

means dividing the plenum chamber into a plurality of compartments;

first blower means for supplying ambient cooling gas to at least one ofsaid compartments for passage through said porous grate means and thebed of material for cooling the material;

first recirculation means for exhausting at least some of the ambientcooling gas from said material chamber after it passes through thematerial and recirculating it to at least one of said compartments forpassage through the porous grate and material for cooling the material;and

second recirculation means for exhausting at least some of the ambientcooling gas from said material chamber after it passes through thematerial and recirculating it to at least one of said compartments forpassage through the porous grate and material for cooling the material;

said second recirculation means being adapted to exhaust from saidmaterial chamber at least some of The total quantity air in Nm /kg ofmaterial which is returned to the kiln as combustion air is 0.31 0.450.14 or 0.90 Nm lkg. The total air used for cooling the material is thesum of the volume of air supplied to the compartments 44 to 54 which is2.92 Nm /kg or about three times the volume returned to the kiln. Thevolume of ambient air supplied to the system by blowers 56 and 66 equalsthe volume returned to the kiln.

It should be apparent from the foregoing that with the recirculationsystem of the present invention, the volume of air used to cool thematerial can be maintained at an effective level of about three timesthe amount of air which may be returned to the furnace without requiringventing to atmosphere. The need for expensive, high efficiency dustcollectors has been eliminated. The collectors 82 and 96 need only berelatively inexpensive mechanical collectors.

It is intended that the foregoing be merely a description of a preferredembodiment and that the invention be limited solely by that which iswithin the scope of the appended claims.

lclaim:

1. Apparatus for cooling hot particulate material such as cement clinkerdischarged from a furnace such as a kiln comprising:

the cooling gas which has been recirculated through said secondrecirculation means whereby a mixing of ambient cooling gas andrecirculated cooling gas is achieved.

2. The apparatus of claim 1 further comprising conduit means forconducting at least some of the cooling gas from said material chamberto a furnace after it passes through said material.

3. The apparatus of claim 2 further comprising heat exchanger meansmounted in said second recirculation means for cooling the gas which isexhausted from said material chamber.

4. The apparatus of claim 3 wherein said means dividing said plenumchamber into compartments is positioned so that at least some of thecooling gas recirculated through said second recirculation means isconducted to a furnace by said conduit means.

5. The apparatus of claim 4 wherein said cooling gas recirculatedthrough said first recirculation means is supplied to a compartmentpositioned so that the gas is conducted to a furnace by said conduitmeans.

6. The apparatus of claim 5 further comprising second blower means forsupplying ambient cooling gas to at least one of said compartments forpassage through said porous grate means and bed of material.

8. The apparatus of claim 7 wherein each of said first and secondrecirculation means includes means for supplying ambient air to thecooling gas after it is exhausted from the material'chamber and beforeit is recirculated to said compartment.

9. The apparatus of claim 8 further comprising dust collector meansmounted in each of said first and second recirculation means.

10. The apparatus of claim 9 wherein said second recirculation meansincludes hood means mounted in said material chamber.

1. Apparatus for cooling hot particulate material such as cement clinkerdischarged from a furnace such as a kiln comprising: a housing having aninlet for material to be cooled and an outlet for cooled material;porous grate means mounted in and dividing said housing into an uppermaterial chamber and a lower plenum chamber; said porous grate meansbeing adapted to support a bed of material in the material chamber;means dividing the plenum chamber into a plurality of compartments;first blower means for supplying ambient cooling gas to at least one ofsaid compartments for passage through said porous grate means and thebed of material for cooling the material; first recirculation means forexhausting at least some of the ambient cooling gas from said materialchamber after it passes through the material and recirculating it to atleast one of said compartments for passage through the porous grate andmaterial for cooling the material; and second recirculation means forexhausting at least some of the ambient cooling gas from said materialchamber after it passes through the material and recirculating it to atleast one of said compartments for passage through the porous grate andmaterial for cooling the material; said second recirculation means beingadapted to exhaust from said material chamber at least some of thecooling gas which has been recirculated through said secondrecirculation means whereby a mixing of ambient cooling gas andrecirculated cooling gas is achieved.
 2. The apparatus of claim 1further comprising conduit means for conducting at least some of thecooling gas from said material chamber to a furnace after it passesthrough said material.
 3. The apparatus of claim 2 further comprisingheat exchanger means mounted in said second recirculation means forcooling the gas which is exhausted from said material chamber.
 4. Theapparatus of claim 3 wherein said means dividing said plenum chamberinto compartments is positioned so that at least some of the cooling gasrecirculated through said second recirculation means is conducted to afurnace by said conduit means.
 5. The apparatus of claim 4 wherein saidcooling gas recirculated through said first recirculation means issupplied to a compartment positioned so that the gas is conducted to afurnace by said conduit means.
 6. The apparatus of claim 5 furthercomprising second blower means for supplying ambient cooling gas to atleast one of said compartments for passage through said porous gratemeans and bed of material.
 7. The apparatus of claim 6 wherein saidfirst blower means is adapted to supply ambient cooling air to acompartment adjacent said outlet and said second blower means is adaptedto supply cooling air to a comparTment adjacent said inlet.
 8. Theapparatus of claim 7 wherein each of said first and second recirculationmeans includes means for supplying ambient air to the cooling gas afterit is exhausted from the material chamber and before it is recirculatedto said compartment.
 9. The apparatus of claim 8 further comprising dustcollector means mounted in each of said first and second recirculationmeans.
 10. The apparatus of claim 9 wherein said second recirculationmeans includes hood means mounted in said material chamber.